This relates generally to imaging devices, and more particularly, to imaging devices with backside illuminated image sensors having application-specific auto-focus pixels.
Image sensors are commonly used in electronic devices (sometimes referred to herein as imagers) such as cellular telephones, cameras, and computers to capture images. Conventional image sensors are fabricated on a semiconductor substrate using complementary metal-oxide-semiconductor (CMOS) technology or charge-coupled device (CCD) technology. The image sensors have arrays of pixels. Each pixel has a photosensor such as a photodiode. Conventional image pixel arrays include frontside illuminated image pixels or backside illuminated image pixels.
Image pixels are fabricated on a semiconductor substrate using complementary metal-oxide-semiconductor (CMOS) technology or charge-coupled device (CCD) technology. The image sensors may include photodiodes and other operational circuitry such as transistors formed in a front surface of the substrate. Metal routing lines and metal vias may be formed over the front surface of the substrate. In addition to capturing images of a scene, some imagers may be capable of performing other functions. Imagers can sometimes include application-specific pixels that are capable of generating signals for performing auto-focusing operations with the imager.
In general, received image light needs to be blocked over some incident angles in order for application-specific pixels to be used for auto-focusing. In frontside illuminated image sensors in which image light is received by the photodiodes through the front surface of the substrate, some angles of incident light are blocked by the metal routing lines at the front side of the substrate. However, in conventional image sensors, there are no metal lines formed over the backside of the substrate, making it difficult for backside illuminated sensors in which image light is received by the photodiodes through the back surface of the substrate to perform auto-focusing operations.
It would therefore be desirable to be able to provide imaging devices with improved backside illuminated image sensors.